Cisco Internetworking Design Guide

An internetwork requires many protocols and features to permit scalability and manageability without constant manual intervention. Large internetworks can consist of the following three distinct components:
Campus networks, which consist of locally connected users in a building or group of buildings
Wide-area networks (WANs), which connect campuses together
Remote connections, which link branch offices and single users (mobile users and/or telecommuters) to a local campus or the Internet. This design guide applies to each aspect of networking.